Communications systems and more specifically selective messaging systems and units or receivers are known. Such selective messaging systems having scheduled operating channels are also known. A scheduled operating channel requires a time reference for the channel that is known to the system and known within specified limits to units operating on the system. Such scheduled operating channels allow the system and units to coordinate activity so as to balance channel activity while allowing individual units to remain inactive or asleep much of the time. This inactive or sleep state allows the selective messaging units (SMUs) to conserve power or battery resources.
However the SMU can utilize significant battery power when searching for a channel prior to the time reference for the channel being determined. Alternatively battery power can be preserved to some extent at the cost of large delays in locating and locking to a channel. Various strategies have been developed that largely trade latency for battery resources during this search however none have been satisfactory at addressing both requirements.
Present selective messaging systems have added an additional degree of complexity commonly referred to as roaming wherein a given SMU can be required to roam from one area or system to another area served by another system. The different system often have different operating channels that are scheduled according to a different time references. The SMU will need to lock to these different operating channels as the SMU roams from area to area. Clearly a need exists for apparatus and methods that allow selective messaging units to switch operating channels having different time references with minimal latency and battery consumption.